This invention relates to compensating rotors used in continuous-flow centrifuge systems. More specifically, it relates to improvements which facilitate high speed operation of compensating rotors in continuous-flow centrifuge systems.
The application of centrifugal force is widely used in the processing of blood and other biological suspensions. It provides a convenient means for sorting and classifying particulates on the basis of buoyant density differences and for retaining particles subjected to opposing hydrodynamic forces. As Illustrative example of such usage is the continuous-flow washing technique for the deglycerolization of red blood cells.
In flow-through centrifuges, such as those marketed by Fenwal and Haemonetics, centrifugal force is employed to retain the red cell mass in the periphery of a processing container spinning at 3000-4000 rpm while saline solutions of decreasing tonicity are passed continuously through cells at about 150-200 ml/min. in a direction countercurrent to the centrifugal field. In both cases, the fluid exchange is effected in a more or less aseptic fashion by means of a rotary seal.
There are several disadvantages associated with the rotary seal arrangement in blood processing applications. The possibility of contaminants passing between the seal faces exists. Consisting, as it does, of an assembly of precisely machined components of specialty materials, the seal represents a major contribution to the fabrication and quality control costs of the blood processing container, which is designed to be a disposable item. In addition, the seal may impose flow limitations, and high shear rates at the seal juncture may damage the more labile blood components.
A recent advance in centrifugal apparatus development allows continuous-flow blood processing without rotary seals. The "compensating rotor" is a mechanical device which permits the exchange of fluids between a stationary system and a rotating system via an integral tubing loop. The absence of the seal eliminates the contamination risk and permits substantially increased flow rates (&gt; 1 liter/min.) with a corresponding reduction in processing time per unit of cells washed. Such an apparatus is useful not only in deglycerolization, but also in various other modes of centrifugal blood processing, including component separation and pheresis applications.
The effect of the 2:1 relative rotation utilized in the operation of conventional twist compensating devices is well known in the art. Illustrations of the application of this principle are found in U.S. Pat. Nos. 2,831,311 and 3,586,413.
The N.I.H. blood centrifuge of the type described in the article by Y. Ito, et al., "New Flow-Through Centrifuge Without Rotating Seals Applied To Plasmapheresis," Science 189, p. 999 (1975) employs 2:1 rotation to effect fluid transfer into a rotating processing container. Similarly, the same principle is utilized in the centrifugal liquid processing system disclosed in U.S. Pat. No. 3,986,442.
It is noted, however, that each of the above prior art devices is somewhat limited in its ability to operate at high rotational speeds. The primary reason for this shortcoming is that each of these devices is inherently unbalanced. As a result, these devices are susceptible to mechanical failure due to the vibration effects experienced at the higher rotational speeds.
It is apparent that the major limitation inherent in each of the prior art devices is its vulnerability at high rotational speeds, due to the 2:1 relative motion between the rotary components, and the associated vibration effects experienced by the mechanical components of the system. Since operating speeds of 3000-4000 rpm are required for effective and economical processing of blood, this is a significant limitation. The need for a continuous-flow centrifuge system capable of operating at 3000-4000 rpm is especially acute in the blood processing industry.
Accordingly, it is an object of the invention to provide a compensating rotor for use in a high-speed continuous-flow centrifuge system. More specifically, it is an object of the invention to overcome the aforementioned difficulties by providing means to inherently balance the compensating rotor in order to minimize the unwanted vibrational effects associated with the operation of conventional twist compensating devices.
It is a further object of the invention to provide a novel inherently symmetrical epicyclic reverted gear train having a minimum number of components which satisfies the requisite 2:1 rotational requirement for a self untwisting mechanism.
It is still a further object of the invention to provide means to share the load between the gears comprising the rotor drive system.